Identifying False Echo Returns - Raymarine H6 Owner's Manual

81238_1.book Page 144 Thursday, September 16, 2004 2:49 PM
144 Raymarine H6 - Owner's Manual
However, with experience the approximate size of different objects can be
determined by the relative size and brightness of the echoes.
Some targets, such as buoys and small boats, can be difficult to differentiate, since
they bob and toss about in the waves and do not represent a consistent reflecting
surface. Consequently, these echoes have a tendency to fade and brighten, and at
times, to disappear momentarily. Buoys and small boats often resemble each
other, but boats can usually be distinguished by their motion.
Not all radar echoes are produced by hard navigational items. Some echoes may
be received from irregularities on the surface of the water, particularly at close
range (sea clutter), or from rain or snow either around the boat or in the distance.
In addition, some echoes may be indirect returns to the radar scanner, providing
false echoes or multiple echoes.
The effects of many false echoes can be minimized, and the target presentation
clarified.

Identifying false echo returns

Not all echoes are direct returns to the radar antenna. Occasionally signals appear
at positions where there is no actual target. These are called false echoes, and
may be caused by side lobes, ghost images, indirect echoes or multiple echoes.
This section briefly describes the echo patterns that can be produced by false
echoes and the likely cause. It should be noted that the radar operator, through
observation, practice, and experience, can generally detect these conditions very
quickly. These effects can usually be minimized using the radar controls.